Heterogeneous recombination of atomic bromine and fluorine

Recombination coefficients (gamma) of Br and F atoms have been measured for crystalline Si, quartz, photoresist, anodized aluminum, poly-Si, WSix, tun gsten and stainless steel surfaces for a range of temperatures. The gamma(B r) and gamma(F) values are compared to our previously reported measurements of gamma(Cl) [G. P. Kota, J. W. Coburn, and D. B. Graves, J. Vac. Sci. Tec hnol. A 16, 270 (1998)]. In general, the Br-, Cl- and F-atom recombination coefficients decrease as the surface temperature increases. The gamma(Br) v alues are similar to the gamma(Cl) values for the various surfaces. At room temperature, gamma(Br) is highest (> 0.4) for stainless steel and tungsten , moderate (0.1-0.4) for poly-Si, WSix and anodized Al, and lowest (< 0.05) for c-Si, quartz and photoresist. However, gamma(F), at room temperature, is no greater than 0.05 for all the surfaces. gamma(F) increases slightly a s the temperature is decreased to 80 K but is still below 0.1 for all the s urfaces. The recombination coefficient data as a function of temperature fo r all surfaces are fit to a phenomenological model developed previously for gamma(Cl) (see the above reference). The model assumes that the incident h alogen atoms physisorb on a surface that is saturated with chemisorbed halo gen atoms. The physisorbed atoms are assumed to diffuse on the surface and either desorb before recombining or recombine and then desorb. The recombin ation rate is assumed to be first order in physisorbed atom coverage. (C) 1 999 American Vacuum Society. [S0734-2101(99)04701-6].